We propose to conduct a pilot study for the prospective investigation of the early stages of cognitive decline in patients with Parkinson's disease and their relation with diet, lifestyle factors, and APOE genotype. Specific factors that will be addressed include cigarette smoking, caffeine consumption, dietary antioxidants, use of anti-inflammatory drugs, and, in women, use of postmenopausal hormones. The investigation would take advantage of two large prospective cohorts: the Health Professionals Follow-up Study (HPFS; 51,529 male health professionals followed since 1986), and the Nurses' Health Study (NHS; 121,600 female registered nurses followed since 1976). The occurrence of incident cases of PD in these cohorts is already being documented as part of an NIH funded study (we have confirmed 470 cases, 250 in men and 220 in women, and follow-up is ongoing). Moreover, diet and other lifestyle factors have been repeatedly assessed in these populations, and cognitive tests have already been administered to several thousands of NHS participants without PD (as part of a separate project). Blood samples or cheek-cell samples for DNA analyses have already been collected from most participants. Cognitive assessment will be accomplished by administering seven tests of cognitive function: the Telephone Interview for Cognitive Status (TICS), the East Boston Memory Test (EBMT, immediate and delayed recall), a category fluency test, a letter fluency task, a digits backward test, and a delayed recall of the 10-word list given in the TICS. The interview will be conducted by telephone and take approximately 20-25 minutes to complete. As part of the proposed project, we will administer these tests to men and women with PD and age-matched healthy controls.